The present invention relates generally to improving the corrosion resistance of zirconium alloy based components in nuclear reactor environments. More particularly, improved stainless alloy compositions are disclosed that reduce the shadow corrosion effect occasionally observed in zirconium alloy components positioned adjacent to stainless components in nuclear reactors.
Corrosion studies of components used in environments subjected to nuclear irradiation have shown enhanced corrosion in various zirconium alloy based components that are positioned adjacent to certain stainless steel, platinum, copper, hafnium and yttrium based components. This enhanced corrosion is manifested by a so-called "shadow effect" that takes the form of a region of enhanced corrosion in the zirconium component that occurs immediately adjacent to the shadowing component. In some cases, the enhanced corrosion can potentially limit the useful life of the zirconium alloy based component. The applicants have determined that there is considerable evidence that a constituent of the "shadowing" material becomes activated and that beta particles emitted by the activated shadowing component are the cause of this increased corrosion (i.e. shadow effect corrosion). This observation has been confirmed, for example, by Lemaignan in his article entitled "Impact of .beta.- Radiolysis and Transient Products on Radiation-Enhanced Corrosion of Zirconium Alloys", Journal of Nuclear Material, Vol. 187 1992 p. 122-130. Two possible mechanisms by which beta particles can cause increased corrosion are the production of irradiation damage in the oxide present on the surface of the zirconium alloy component, and the production of local transient radiolytic species in the coolant water.
In boiling water reactors, stainless steel is used in many core components. Thus, the applicants have observed shadow effect corrosion in several components. It is therefore an object of the present invention to eliminate or at least reduce the shadow effect caused in zirconium based components that are situated adjacent to stainless alloy components within a nuclear reactor.